The present invention relates in general to cutting an object from a sheet using a fluid jet stream. More particularly, the present invention relates to supporting the sheet (e.g., a glass or ceramic sheet) while the object (e.g., an annular disk substrate for use in a data storage device) is cut from the sheet.
A typical disk drive data storage system includes one or more data storage disks for storing data, typically in magnetic, magneto-optical or optical form, and a transducer used to write and read data respectively to and from the data storage disk. The data storage disks are typically coaxially mounted on a hub of a spindle motor. The spindle motor rotates the data storage disks at speeds typically on the order of several thousand or more revolutions-per-minute. Digital information, representing various types of data, is typically written to and read from the data storage disks by one or more transducers, or read/write heads, which are mounted to an actuator assembly and passed over the surface of the rapidly rotating disks.
In a typical magnetic disk drive, for example, data is stored on a magnetic layer coated on a disk substrate. The disk substrate is typically aluminum-based (e.g., aluminum magnesium alloy coated with NiP), glass (e.g., aluminosilicate glass), ceramic (e.g., alumina, silicon carbide or boron carbide), or composite (e.g., aluminum boron carbide composite).
Typically, the glass or glass-ceramic disk substrate is made by traditional machining techniques. One such technique is the mechanical scribe and break method, followed by edge grinding. These traditional machining techniques require costly, high precision tooling to make the exact dimensions of a disk substrate. In addition to being costly, these traditional machining techniques form an edge on the disk substrate that requires a subsequent edge polishing process. That is, the brittle fracture created by these traditional machining techniques must be polished out of the edge surfaces of the disk substrate. Damaged edges result in disk substrates having weakened structural integrity.
A non-traditional technique for making the glass or glass-ceramic disk substrate is the laser scribe and break method. Initially, during a laser scribe step, a blank from which the disk substrate is to be formed is scribed by a laser. Then, during a thermal breakout step, the blank is heated and a crack is initiated along the scribe line. This method produces a disk substrate having a very clean edge with right angle corners. However, the laser scribe and break method has several disadvantages. For example, the method is inherently slow due to its sequential two step nature and because only one part may be machined at a time. In order to equal the output of traditional machining techniques, the laser scribe and break method requires many systems operating in parallel. This increases costs. Another disadvantage relates to the right angle corners produced by the laser scribe and break method. These corners may need to be rounded or at least chamfered. Thus, the pristine edge may require subsequent processing that potentially negates its edge finish. Yet another disadvantage of the laser scribe and break method is that the laser must be tuned for each formulation of the disk substrate. In some cases this may require replacement lasers that have different operating wavelengths, thereby increasing cost and delay.
Yet another disadvantage of the laser scribe and break method is the nub created at the crack initiation point. An extra edge polishing process is required to remove this nub.
There exists in the data storage system manufacturing industry a keenly felt need to provide an enhanced machining technique for making disk substrates. There exists a further need to provide such an enhanced machining technique for making disk substrates that permits improvement in production cycle times, costs and/or disk substrate quality.
An object of the present invention is to provide an enhanced machining technique.
Another object of the present invention is to provide an enhanced machining technique for making a disk substrate.
Yet another object of the present invention is to provide an enhanced machining technique for making a disk substrate that permits improvement in production cycle times, costs and/or disk substrate quality.
These and other objects of the present invention are achieved by a fluid jet cutting method and apparatus for cutting an object from a sheet. In an exemplary embodiment, a fluid jet stream is directed against a glass sheet to cut an annular disk substrate for use in a data storage device. The sheet is supported by first, second and third support members. The support surfaces of the second and third support members are respectively positioned inside central openings in the first and second support members. A vacuum pulls the sheet against the support surface of at least the second support member.
Preferably, a plurality of central openings in the first support member accommodate a plurality of second and third support members, whereby a plurality annular disk substrates are cut from the sheet. This permits improvement in production cycle times and costs. For example, a plurality of fluid jet streams may directed against the sheet to simultaneously cut a plurality of annular disk substrates.
The sheet preferably includes a plurality of layers removably adhered to one another, whereby a plurality of annular disk substrates are simultaneously formed by a single fluid jet stream. This arrangement permits improvement in production cycle times and costs.
A protective layer may cover a portion of at least one surface to the sheet. This permits improvement in disk substrate quality. For example, the protective layer may be used to protect the surface of the annular disk substrate adjacent to the cut from being damaged by overspray of the fluid jet stream and chipout caused as the fluid jet stream exits the sheet.